1. Field of Invention
This application relates to a device for the production of sound, specifically a radically new type of a rotary loudspeaker driver with a unique diaphragm.
2. Prior Art
Conventional drivers have a voice coil, constructed of windings of a conductive wire, attached to a diaphragm. The voice coil carries an electrical signal which creates a magnetic field. That field interacts with the magnetic field of a permanent magnet. The goal is to cause the voice coil and therefore the diaphragm to move in response to the frequency and amplitude of the electrical signal. The diaphragm moves the medium it is immersed in, typically air, and produces an output which is the acoustic analogue of the electrical signal.
In the case of a cone speaker or a dome speaker the voice coil wire is wound around a tube which extends perpendicular to the plane of the diaphragm. In the case of a planar magnetic driver the voice coil is embedded in or covers most of the surface of the diaphragm. The permanent magnets are held away from and parallel to the plane of the planar magnetic diaphragm.
In all cases, the cone and the dome and the planar magnetic drivers the diaphragm is held at its edge to a frame, also called a basket in the cone and in the dome speaker. Also attached to the frame are a permanent magnet and a set of pole pieces. The pole pieces serve to focus the magnetic field of the permanent magnet around and inside of the voice coil. This cavity formed by the magnets and the pole pieces is referred to as a magnetic gap.
In the design of the conventional cone driver a flexible and air-tight ring, called a surround, connects the large edge of the cone to the frame. The surround is often made of rubber or foam. A second smaller ring called the spider connects to the neck of the cone which is also where the voice coil attaches to the cone. The spider's function is to also center the voice coil in the magnetic gap and provide a spring function to return the cone assembly to its rest position or home position.
Traditionally the surround most always serves to acoustically seal the diaphragm to the frame and thus the diaphragm to a speaker baffle. The baffle is the mounting surface to which most driver(s) attach. The baffle is most always the front side of the loudspeaker box that encloses the back of the drivers. This whole loudspeaker box assembly being called a loudspeaker cabinet or a loudspeaker box.
The surround contributes to the reproduction of sound of each driver. The surround moves with the diaphragm. The surround by the nature of its function is of a different material from the diaphragm. It is elastic and its different acoustic properties will add its own acoustic character to the sound of the driver.
In traditional loudspeaker designs the loudspeaker box serves to modify and or control the back radiation from the driver. Traditionally the main function of the loudspeaker box is to keep the back radiation from meeting the front radiation in phase and canceling out all sound by destructive interference or phase cancellation. Planar magnetic speakers sometimes do without a loudspeaker box due to their sheer size which minimizes the said phase cancellation.
The boxes are a source of great expense in the construction of loudspeakers and consume millions of board feet of lumber. The boxes require much engineering to eliminate resonances and vibrations that they are prone to. The boxes are a major source of diffraction of sound waves off of the surface of the box and which serves to distort the sound waves.
In the planar magnetic design it is the edge of the diaphragm that is fixed to the frame. Therefore the diaphragm serves the double and contradictory function of being the rigid diaphragm and the surround that is flexible. The planar magnetic diaphragm moves more like a drum head than a piston. This nonlinear movement is minimized only by its large surface.
It is the very nature of the surround's elasticity that invites nonlinear movement when the diaphragm is moving. The thin and flexible diaphragms of loudspeakers flex while operating. When combined, the materials used for the surrounds and spiders and diaphragms these materials' nonlinearities are compounded. The whole system is often operating outside of the narrow linear envelope of accurate reproduction. These distortions are sometimes considered euphonic or non-irritating but are definitely distortions. The surround and the spider are flexible and are asked to perform the contradictory functions of providing spring and stiffness.
The flexing of traditional pistonic diaphragms is a result of designing for the thinnest and lightest materials to construct diaphragms. Thicker and therefore more rigid diaphragms are inherently more linear but put too large a mass burden on the surrounds of rubber and foam of the conventional cone and dome pistonic drivers.
The whole flexible cone diaphragm and surround and spider suspension system is an easily constructed and understood compromise which is the basis of the traditional design approach to sound production drivers. Its visual analogue to the ear drum has an immediate emotional appeal and is conceptually easy to understand for every school child.